An LCD is a sort of optical shutter, and the optical shutter is created for each pixel. Light is controlled by the opening and closing of the optical shutter, whereby an image is displayed. If a color film through which visible light is transmitted is applied to each pixel, that color will be displayed when the shutter is open. If, as a color film, the red (R), green (G), and blue (B) which are the primaries of an additive color process are controlled as a single block, color display will become possible.
In the color filter for an LCD, usually R, G, and B pixels are regularly arrayed and the respective pixels are fringed with black matrixes. Each pixel can be made by various processes, such as a dyeing process of dyeing a pattern formed by photolithography, a printing process of printing a pattern directly on a transparent plate, an elecrodeposition process of providing a transparent electrode pattern on the surface of a transparent substrate and depositing coloring matter on the surface of the pattern together with vehicle, or a pigment dispersing process of forming a photo polymeric composition contained with a pigment into a pattern with photolithography.
Liquid crystal displays require light-resisting property and heat-resisting property from the viewpoint of stability and lifetime and, on the other hand, there is a demand for a color filter with high contrast and transparency from the viewpoint of power saving and display quality. The coloring matter of a color filter is gradually shifted from dyes to pigments in view of light-resisting property and heat-resisting property, and although a pigment has presently been used, the pigment is composed of particles, so the contrast and transparency that are obtained by light scattering are insufficient. Therefore, an attempt to solve the problem by reducing a particle diameter has been made and contrast has reached a nearly satisfactory level with a particle diameter of 0.1 to 0.05 micron.
For the transparency of a color filter, the matching between the emitted wavelength of a light source and the transmitted wavelength of a color filter is also important, apart from the particle diameter of a pigment. As a light source for liquid crystal displays, a cold-cathode tube called a 3-wavelength tube is usually used, and for example, the emitted wavelength of red is 610 nm.
Since Simple primary color a spectral characteristic desirable for such a color filter and it is known to obtain a desired spectral characteristic by mixing pigments. In particular this problem exists for the red pigment of a color filter.
As a red pigment, C. I. Pigment Red #177 and "primary yellow" (C. I. Pigment Yellow #139) are employed in. The spectral characteristics of those pigments are shown in FIG. 1. (C.I. refers to the Color Index published by The Society of Dyers and Colourist and the American Association of Texitle Chemists and Colorists).
As is evident in FIG. 1, C. I. Pigment Red #177 (indicated by (1) in FIG. 1), as it is, cannot be applied to a color filter because it has high transmittance near 380 to 530 nm and will degrade color purity (color closing to mulex as blue component mixes in red). Hence, primary yellow (C. I. Pigment Yellow #139 (indicated by (2) in FIG. 1)) where transmittance is relatively low in a wavelength region near 380 to 480 nm is mixed as a complementary color in order to enhance color purity. However, in this method the matching with a light source is insufficient and the mixed color will become dark red.
Also, for C. I. Pigment Red #244 (indicated by (3) in FIG. 1), the transmittance is higher with a wavelength of 610 nm but the y value of a chromaticity value is greater than a target value, and it is so-called red tinged strongly with yellow and is out of a usable range.
Hence it is desired to have a photo polymeric composition which can provide a color filter with an improved transmittance or transparency of a red region and an improved color purity.